Simulators

[ViperSniper]

Anyone ever have problems with running rich after modifying there exhaust and replace there rear 02 sensors with simulators to correct the problem?
I was told this can be a problem because of the added heat from high flow cats or opened exhaust, your car may or may not throw a code but your computer will go into a safe mode and run a little rich with a small loss of hp and the rear 02 simulators fix it.


VS

[mrr23]

never heard of that.

[35thAnniZ28]

alright man ..check this out....right now ..im running rich as hell...cuz i just put long tubes and didnt bother buying the extensions for the rear(bought em for the front ones)...so stoopid me thought the car was gunna go fast with headers..nope!.....im dirtying my spark plugs with extra unnecesary fuel....and yes i already bought the sims...ill input in a week if they work ...

[ViperSniper]

alright man ..check this out....right now ..im running rich as hell...cuz i just put long tubes and didnt bother buying the extensions for the rear(bought em for the front ones)...so stoopid me thought the car was gunna go fast with headers..nope!.....im dirtying my spark plugs with extra unnecesary fuel....and yes i already bought the sims...ill input in a week if they work ...

If 02s are put in the front (before the cats) it will really run terrible you want them after the Cats.

VP

[mrr23]

If 02s are put in the front (before the cats) it will really run terrible you want them after the Cats.

VP

um no you don't. not having rear o2s doesn't change the tune or drive ability. their sole purpose is for the PCM to compare front to rear o2 readings to determine if the cats are working. the front o2s determine correct fueling. to have your PCM trying to set fueling after the cats will be an issue as they are getting filtered readings.

[mrr23]

alright man ..check this out....right now ..im running rich as hell...cuz i just put long tubes and didnt bother buying the extensions for the rear(bought em for the front ones)...so stoopid me thought the car was gunna go fast with headers..nope!.....im dirtying my spark plugs with extra unnecesary fuel....and yes i already bought the sims...ill input in a week if they work ...

how do you know it's rich and not lean? refer to my above post about what he rear o2s job are. if you are still running cats, then it's a good idea to have the rears. this way you'll know when they go bad. other than that, they serve no purpose in the engine's running.

[35thAnniZ28]

hhhmmmm...how do i know if it rich ...well the horrible gas smell..even with cats and no rear sensors...(going to remove em soon..) and i already have o2s in the front....just waiting for the delivery of the sims ..for the back...ill keep it posted

[02z28ls1]

OK- the rear O2 sensors are there to check if the front ones are working. But what happens when the rear are picking up nothing but air? Or are unplugged all together? At least with the simulators installed the computer believes everything is good, but the other scenerio I'm not sure what the result is. Maybe it does more than just set a code.
And yes--- O2 sensors are supposed to be in front of the cats-as stated the rear ones are OBDII diagnostics sensors.

[mrr23]

hhhmmmm...how do i know if it rich ...well the horrible gas smell..even with cats and no rear sensors...(going to remove em soon..) and i already have o2s in the front....just waiting for the delivery of the sims ..for the back...ill keep it posted

running lean will give you that same smell.

[mrr23]

OK- the rear O2 sensors are there to check if the front ones are working. But what happens when the rear are picking up nothing but air? Or are unplugged all together? At least with the simulators installed the computer believes everything is good, but the other scenerio I'm not sure what the result is. Maybe it does more than just set a code.
And yes--- O2 sensors are supposed to be in front of the cats-as stated the rear ones are OBDII diagnostics sensors.

the rears are there to see if the cats are working, not to see if the front 02s are working. the PCM compares the front o2 readings to the rear o2 readings. the rear o2s are supposed to read lower than the fronts. this tells the PCM the cats are working. if the rears are reading the same, or not low enough, then the SES light comes on for codes P0420 and P0430.


again, the rear do nothing in changing the fueling for the motor. mine are unplugged and codes turned off.

[35thAnniZ28]

put in sims...codes turned off....problem solved

[02z28ls1]

the rears are there to see if the cats are working, not to see if the front 02s are working. the PCM compares the front o2 readings to the rear o2 readings. the rear o2s are supposed to read lower than the fronts. this tells the PCM the cats are working. if the rears are reading the same, or not low enough, then the SES light comes on for codes P0420 and P0430.


again, the rear do nothing in changing the fueling for the motor. mine are unplugged and codes turned off.

Then how did it change the way the engine was running? After supplying the computer with a proper (if simulated) rear o2 output the codes would , of course, turn off- but notice how his engine went back to running proper. I will quote from the factory service manual page 6-1770 under the Engine Controls-5.7 section "The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 HO2S 2 and Bank 2 HO2S 2 (rear)sensors main function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the PCM will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring." Hence the noticeable if slight change in his engine fuel delivery.
Turning off the codes so the computer can't realize a problem also means the computer will not try to compensate for problems. If it isn't perceiving a problem it won't change anything. However if the computer sees trouble codes it could try to compensate depending on the codes being set.
Maybe a technicality but wanted to point out another inaccuracy-the computer looks at the rear O2 for less activity than the front O2. It doesn't compare readings for high or low, just less activity. There will not be as much switching back and forth between lean and rich (activity) behind the convertor when the convertor is working properly.
These computer control systems are much more complex than you give them credit for.

[mrr23]

because you have the codes set off. and while they are on, as the factory servivce manual states, will make a slight adjustment.

this i did not know, but do now. see, i can be taught. i give these computers tons of credit. just don't know every little thing it does.

either way, put simms in or have the codes deleted will do the same thing.

[Mr. Luos]

Expect that sims can still throw a code and having them tuned out won't.

The sims have a preset value to them. They work fine...until for some reason, your front O2 reads more or less A/F ratio than the sim is set up for. Then that lovely SES light returns.

[Steve Crowe]

These computer control systems are much more complex than you give them credit for.

Depends on the year. The "rules" they expect to be obeyed become increasingly strict - especially when they approached the mid-2000 year models. Take a moment to read some of the things we found about 2nd O2 monitoring on our website: http://iecoklahoma.com

Personally we haven't seen much of a problem with the fuel mixture changing if the rear O2 sensors are defeated on a pre-2002 vehicle; however that assumes a decent tune. If the engine is maintaining decent readings at the 1st O2 and sees "acceptable" readings at the 2nd O2 it shouldn't bother changing anything.

The problems start to arise on the newer model years when the PCM expects to see rich/lean readings at the 2nd O2 upon acceleration/deceleration.

[02z28ls1]

I wasn't talking about defeating the rear 02 completely-but the guy had a situation where he didn't have them hooked up (unplugged). The computer wasn't seeing acceptable readings- it wasnt seeing any readings at all! He was getting a code of course-and evidently the engine computer controls were trying to compensate for this. Incidently-I got that info out of a 98 model year service manual (my first Camaro was a 98). That makes the earlier models capable of this also.
My point about the complexity of the computer systems was that to say that the rear 02's don't have any capability of changing fuel trim is flat incorrect. Putting sims in or changing computer flashing is another matter. Sounds like it is more complex to fool the computer in the 2000 and up model year vehicles.

[Steve Crowe]

As I read a '98 Helms I had handy for a different GM engine the descriptions for DTC P0171 & P0172 make no mention that the 2nd O2 sensor could be affecting the reading, however reading on DTC P0137 & P0138 it is worded as if they might.

I think the key here is in the quote "The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 HO2S 2 and Bank 2 HO2S 2 (rear)sensors main function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the PCM will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring."

Curious though is why, if such condition existed, wouldn't the main codes for rich or lean set?

[mrr23]

As I read a '98 Helms I had handy for a different GM engine the descriptions for DTC P0171 & P0172 make no mention that the 2nd O2 sensor could be affecting the reading, however reading on DTC P0137 & P0138 it is worded as if they might.

I think the key here is in the quote "The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 HO2S 2 and Bank 2 HO2S 2 (rear)sensors main function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 millivolt bias voltage for an extended period of time, the PCM will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring."

Curious though is why, if such condition existed, wouldn't the main codes for rich or lean set?

my thought would be the condition for the lean/rich P0171/P0172 would only refer to the front o2s being stagnant for a period of time. P0137/P1038 would refer to the rear o2s stagnating.

[LS1buckey]

I can say first hand that not having the rear o2's hooked up does present drivabilty problems. The sim I bought worked for awhile and the car ran fine but when it stoped and codes for (no activity) on the rear o2's started again the car started lagging real bad, I'm still working through the issue, trying to find better sim(s). I'm having trouble finding some one to tune them out but they do cause problems if they are gone.


Atleast for me they do.

[mrr23]

i remember when i put simms on the wife's car. i had one go bad three days later. only the SES light came on. no drive ability problems. just goes to show not everyone will have the same symptoms. eventually i did put cats back on her car and reinstall the rear o2s.